You can do a line trace to the floor, then use the HitActor’s Z location for your actor.
When I just tried this, the object (basic cube) disappeared half into the ground. This happens because the cube’s pivot is placed at its center. If this happens, the easiest fix is probably to either adjust the mesh itself in whatever tool is used to model the meshes and move its pivot to the floor, or you could move the mesh a bit upwards in the actor viewport.